Zeolite composite membranes obtained by forming a zeolite membrane as a separation membrane on a substrate have been known and have been used as a gas separation membrane or a liquid separation membrane.
Zeolite composite membranes and zeolite laminated composites can also be used as a reaction and separation unit possessing a reaction function and a separation function, by being combined with a certain kind of catalyst or the like. For instance, there is a reaction apparatus (which is called a “membrane reactor”) wherein the above-mentioned reaction and separation unit is provided inside a reactor; and an example thereof is introduced in, for example, Naoji Ito, Chemical Engineering (1997), October.
The membrane reactor having such a constitution can remove, in a reversible reaction system, a produced substance selectively out of the reaction system and, therefore, has an advantage of allowing the reaction to proceed apparently at a conversion exceeding the equilibrium conversion. As a reaction and separation process using the membrane reactor, a xylene isomerization process is disclosed in Japanese Patent Application Kohyo No. 2000-515849.
Incidentally, as an example of the reaction and separation unit, there is known a type in which a catalyst is filled in the vicinity of a porous substrate and/or a separation membrane composed of a zeolite.
Also in E107 of the 66th annual meeting of Kagaku kogakukai, there is disclosed a reaction and separation unit of a type in which a silicalite (a kind of zeolite) is formed on a porous alumina substrate [in this formation, a low-silica MFI type zeolite membrane (hereinafter referred to also as an “MFI membrane”) is formed at the interface between the silicalite and the alumina substrate] and the MFI membrane is utilized as a catalyst.
However, in the above-mentioned reaction and separation unit of a type in which a catalyst is filled in the vicinity of a porous substrate and/or a separation membrane composed of a zeolite, there adds, to the pressure losses of the porous substrate and the separation membrane, a pressure loss of the catalyst-filled layer formed by catalyst filling; therefore, there is a problem that the permeation efficiency of the substance produced by the catalytic reaction of the raw material substance is not good.
Also, in production of the reaction and separation unit of a type disclosed in E107 of the 66th annual meeting of Kagaku kogakukai, there is a problem that it is difficult to control the amount of catalyst and the SiO2/Al2O3 (molar ratio) (hereinafter, when simply “SiO2/Al2O3” is mentioned, it means a molar ratio) of the MFI membrane formed.
Further, when the MFI membrane has been formed on the alumina substrate, there may be a case that defects such as cracks in the MFI membrane may generate under, for example, a high temperature condition, owing to the difference in thermal expansion behavior between the alumina and the MFI membrane, i.e. the zeolite.
The present invention has been made in view of the above-mentioned problems of the prior art, and aims at a zeolite laminated composite which shows a small pressure loss and hardly generates defects such as cracks in the separation membrane even under a high temperature condition, as well as a zeolite membrane reactor of high separation characteristic and high permeability, using the zeolite laminated composite.